Automotive antifreeze consists of a base fluid of ethylene or propylene glycol and water into which are dissolved corrosion inhibitors, antifoaming additives, anti-scaling additives, dispersing agents and a distinctive dye. Virgin glycol-based antifreeze is usually made as a concentrated product (96% glycol and 4% additives and water) and it is used in engines at a lower concentration, diluted by water. Most antifreeze is used at a concentration of 40% to 60% glycol and 60% to 40% water. Making and shipping antifreeze as a concentrated product saves the freight cost of shipping water and reduces shipping costs per unit of concentrated antifreeze. In retail markets, more and more antifreeze is being packaged, shipped and sold as a 50% prediluted product, for consumer convenience.
Used antifreeze is usually contaminated with other used fluids from vehicle service work at a given facility. These fluids include used motor oil, used transmission fluid, used brake fluid, gasoline, and diesel fuel. Although separate disposal containers are usually provided, mechanics and service center employees don't always pay close attention as to which disposal container they are using for which used fluids. Used motor oil combined with lighter hydrocarbons, such as fuel, can form relatively stable emulsions with the water/glycol phase. The oil/hydrocarbon phase is usually less than 5% by volume, so an oil-in-water emulsion is formed.
Pretreatment of glycol-containing waste streams has involved gravity separation in storage without demulsifier assistance, wing-type oil/water separators, weir-type oil/water separators, flocculation/filtration, and simple filtration. All of these approaches are very labor intensive, produce widely varying results, and may leave behind a total hydrocarbon level of approximately 0.5%-1.0%. Residual hydrocarbons at these levels in the feed to the primary treatment may negatively impact the effectiveness of the primary treatment system.